Why Is the Black Hole at the Center of the Milky

Why is the black hole at the center of the Milky Way growing very slowly in comparison to some other black holes?

A) It is much smaller than the black holes in other galaxies.
B) The surrounding gas is too hot.
C) There is no nearby matter that could fall into the black hole.
D) The nearby matter is composed only of positrons, which annihilate with electrons before they can fall onto the black hole.